Generally, HFC-125 does not contain chlorine in the molecule, and thus has very low impact on global warming and ozone depletion. HFC-125, which is an alternative material of chloro-fluoro-carbon or hydrogen-chloro-fluoro-carbon used as conventional coolants, foaming agents or propellants, is mixed with difluoromethane (CH2F2, hereinafter, referred to as ‘HFC-32’) to serve as a material for mixed coolants.
Catalysts for use in the preparation of HFC-125 using chloroethane compounds as raw material are known, almost all of which comprise chromium oxides.
Japanese Patent Laid-open Publication No. Hei. 2-178237 discloses a catalyst for the preparation of HFC-125 using a chloroethane compound, in which the catalyst is exemplified by Cr2O3—BaO—Al2O3, Cr2O3—MgO—Al2O3, Cr2O3SrO—Al2O3, Cr2O3Al2O3, and Cr2O3MgO.
The Cr2O3Al2O3 catalyst is prepared by dissolving Cr(NO3)3.9H2O and water, adding ammonia water with stirring to prepare a precipitate of Cr(OH)3 and Al(OH)3, which is then washed with water, dried and then calcined at 450° C. for 5 hr to obtain Cr2O2Al2O3 powder, forming the powder into a pellet, and then fluorinating the pellet using a gas mixture comprising N2 and HF.
U.S. Pat. No. 6,433,233 discloses Cr2O3/Al2O3, Cr2O3/In2O3, Cr2O3/Ga2O3, Cr2O3/CoO, Cr2O3/NiO, and Cr2O3/ZnO catalysts.
Of these catalysts, the Cr2O3/Al2O3 catalyst is prepared as follows.
First, ammonia water is added to an aqueous solution of Cr(NO3)3 to obtain Cr(OH3)3 precipitate, which is then filtered and dried to obtain Cr(OH3)3 solid, which is then pulverized into Cr(OH3)3 powder. Subsequently, the powder is added to an aqueous solution of Al(NO3)3, allowed to stand for 12 hr, dried, and added with a small amount of graphite to form a pellet. The pellet thus obtained is calcined for 2 hr using N2 gas and then fluorinated using a gas mixture of N2+HF, thus yielding a desired Cr2O3/Al2O3 catalyst.
In this way, according to the conventional processes of preparing a binary chromium oxide catalyst, such as Cr2O3—Al2O3, or a ternary chromium oxide catalyst, Cr(NO3)3 and Al(NO3)3 are dissolved in water, after which the obtained solution is coprecipitated using ammonia water to obtain Cr(OH3)3—Al(OH)3 coprecipitate, which is then calcined to prepare a Cr2O3—Al2O3 catalyst (Japanese
The use of the chromium oxide catalyst (U.S. Pat. No. 6,433,233), resulting from impregnation of binary or ternary oxides, leads to the following selectivity when using HCFC-123 as a starting material.
Selectivity (%)CatalystHFC-125HCFC-124HCFC-123CFC-115Cr2O3—In2O367.114.817.00.11Cr2O3—Ga2O366.914.916.90.17Cr2O3—CoO67.022.38.90.22Cr2O3—NiO65.223.910.70.015Cr2O3—ZnO66.820.812.20.033Cr2O3—Al2O367.022.38.90.22
That is, when the starting material is PCE, the selectivity to HFC-125 is less than 20%. In contrast, the use of HCFC-123 as a starting material results in selectivity to HFC-125 of up to 70%.
Therefore, there is need for the development of a catalyst enabling the conversion of a chloroethane compound and the selectivity to HFC-125 to increase, upon fluorination.